112lect14 - GY 112 Lecture Notes D. Haywick (2006) 1 GY 112...

GY 112 Lecture Notes D. Haywick (2006) 1 GY 112 Lecture Notes Fossil Preservation Lecture Goals : A) The fossil record B) Types of fossil preservation C) Trace fossils Textbook reference: Levin 7 th edition (2003), Chapter 4; Levin 8 th edition (2006), Chapter 6; Lab manual Week 5) A) The fossil record By now you have probably had your fill of fossils. I have. I mean, I like the little beasties, I just can’t handle their names. Fossil taxonomy is pretty “dry”. We have spent considerable time outlining the importance of fossils in interpreting the rock record, but we have failed to discuss just how complete the fossil record is (or isn’t). The lead image on this page was taken from Heck's Iconographic Encyclopedia (1851) and show that fossils were well know back in the 19 th century (source: http://www.dickinson.edu/~nicholsa/Romnat/fossils.htm). But even today, more than 150 years since the publication of Heck’s book, we still have only found a small fraction of all of the beasties that actually lived over the past 600 million years. Oh we have a lot; possibly millions of different animals and plants, but not all of them. No where near all of them Think about all of the creatures

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GY 112 Lecture Notes D. Haywick (2006) 2 that are today inhabit the Gulf of Mexico. All will eventually die, but few will ever make it to the rock record. Most will be eaten by something else before their remains make it to the sea floor. Even if they make it to the seafloor, something living in the sediment (worms, bacteria) will probably devour them. Sea shells are pretty durable, but taken out of a marine setting, they can quickly dissolve away entirely. The odds of any one fossil being preserved long enough for us to find it are very, very low. Fortunately enough have been preserved for us be able to reconstruct most of the Phanerozoic Era. But just remember that the fossil record is anything but complete. The way in which fossils can be preserved is highly variable. The type of preservation depends largely on the material the beastie was composed of and the fluids that they were exposed to. B) Types of fossil preservation Some fossils retain their original mineralogy when fossilized, but not all do. Most marine shells are composed of calcium carbonate (CaCO 3 ). There are 2 different minerals that share this general chemical formula that are used by beasties to make their shells, tests and skeletons: aragonite and calcite. These 2 minerals are polymorphs. That means that they have the same chemical composition, but different crystal structures (see image

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